The desire to operate vehicles with the highest possible driving comfort, also having a high and spontaneous automatic transmission, which can transmit more and more torque, results in continuously, increasing requirements of the functionality of the vehicles equipped with electro-hydraulic steering and an automatic transmission. A higher ability to transfer the torque of an automatic transmission reduces a flow-torque-resolution in the area of electro-hydraulic actuators, which can only be solved through a large and unreasonable effort.
In addition, the increased effort is a result of the development of new methods of manufacturing, whereby manufacturing tolerances have to be revisited at the manufacturer site and maybe even to be tightened. Also, the additional development of implementations become necessary, through which the remaining manufacturing tolerances, or their effect in regard to the behavior during the operation of automatic transmissions, can possibly be reduced to an absolute minimum.
Both scenarios will usually result in an increased effort and cost for the control, monitoring, and the manufacturing process, which is not intended and not desirable.
In an article in Technische Mitteilungen 97 (2004), Volume 1, Page 4 to 13, “Implementation of Electro-Magnetic Actuators into the System Architecture of Vehicles,” a cost effective process and implementation is described using electro-mechanic and electro-hydraulic transponders in passenger vehicles, which generally are being used in hydraulic aggregates as proportional pressure valves or flow control valves. In mechanical systems, actuators based on switching and proportional magnets are often being used to perform the lock or release function for the activation of devices.
The dynamics and the precision of a machine, operated through an electro-hydraulic concept, is generally determined by the precision and flow control of such actuators, also by trying to optimize the dynamics and precision of the flow control.
A usually unavoidable friction generated when using pilot valves is often the main reason for a finite durability of the system and it works against an intended system optimization of the actuators. As an example, the plotted graph of a proportional pressure reduction valve shows, when describing the relationship between output pressure at a control output of a valve, under a constant pressure feeding condition at the input and the return path and the current in the coil of an electro-magnetic actuator, that an offset exists between the rising, increasing, current slope and the falling, descending, current slope, caused through mechanical friction in the valve, generally known in the art as the hysteresis. The width of the hysteresis of an actuator functioning as a valve limits the ability of reproducing the actuator position and also limits the functionality of the system components, connected to the actuator, which follow.
To reduce the friction and minimize the hysteresis of the valve and using a commonly known valve in the art and technology, a so called Dither-Modulation, where the current in the coil of the electro-mechanic valve being modulated by a Dither-Signal, which comprises a low frequency square wave in the range of 100 Hz to 1000 Hz. The actuator anchor and the electro-mechanical parts of the actuator, physically connected to the valve gate, are undergoing a vibration. The amplitude of the Dither-Signal will be adjusted in a way to levels that there are no unwanted fluctuations caused with regard to the pressure in the hydraulic system. The vibration causes a reduction of the friction in the valve and, therefore, a reduction of the hysteresis, which improves the resolution of the system and the reproducibility of the actuator operation and position.
A disadvantage, however, is the fact that the Dither-Signal modulation, and its low frequency vibration, cause an increased wear in the area of an electro-hydraulic valve system and, therefore, it reduces the life of a valve.